The present invention relates to an optical disc playback apparatus for playing back images and sounds by reading out image and sound information recorded in an optical disc, such as a DVD (digital versatile disc) or the like. More specifically, the present invention relates to an optical disc playback apparatus having neither playback function nor outputting function for DTS (digital theater system) sound.
Traditionally, an optical disc such as a DVD or the like has compressed data for various types of sound, such as LPC (linear pulse code modulation) sound, Dolby Digital sound, MPEG (moving picture coding experts group) Audio sound and DTS sound, in a so-called multiple audio signal stream. At present, optical discs in which the DTS sound is recorded in the initial signal stream are increasingly used.
Furthermore, it is known that a certain type of an optical disc playback apparatus is not equipped with DTS decoder for playing back the DTS sound, which DTS decoder is installed in an audio decoder for playing back sound, or it is designed such that the DTS sound cannot be output, because the patent license fee for the usage of the DTS decoder is not paid.
In such an optical disc playback apparatus having neither the playback function nor the outputting function for the DTS sound, a user is usually unable to select the playback of DTS sound, wherein, in the initial setting, i.e., in default before shipping from a factory, the playback apparatus is such that a sound other than the DTS sound is automatically selected in the initial state of playback after the power supply is turned on. Accordingly, no DTS sound signal is supplied from the sound output terminal in the initial state of playback after turning on the power supply, because no compressed data for the DTS sound are supplied to an audio decoder. See, for example, Japanese Unexamined Patent Application Publication Nos. 2001-28167 and No. 2002-170330.
When, however, a user tries to playback an optical disc in which, for instance, LPCM, Dolby Digital, MPEG Audio and DTS sounds are recorded, using a conventional optical disc playback apparatus having neither playback function nor outputting function for the DTS sound, it is preset such that a sound other than the DTS sound (normally LPCM) is automatically selected in the state of playback. Therefore, no DTS sound but the LPCM sound is output, even if an optical disc including DTS content is played back. This causes the user to receive his unpleasant feeling. In the case when he wishes to output the Dolby sound, he has to carry out an operation for selecting the Dolby sound as a type of sound to be listened.
For instance, the Dolby sound is selected, either in the setting menu on the side of the apparatus or in the disc menu in the optical disc including the DTS content. In the case when the Dolby sound is selected in the disc menu, the sound to be listened changes over from DTS to Dolby, if defaulted to the DTS sound. Accordingly, a troublesome operation is required to select the Dolby sound in the conventional optical disc playback apparatus, thereby providing a somewhat inconvenient operation thereof.
In the prior art of Japanese Unexamined Patent Application Publication No. 2001-28167, the type of encoding the data, which are recorded in an optical disc, is stored, after allocating them to the content information, so that the playback of information, in particular, audio information corresponding to the type of encoding is carried out by identifying the type of encoding in the disc when the disc is loaded. In this prior art, it is found that the DTS sound is discriminated from the PCM sound. However, the Dolby sound is not described anywhere in the specification. Consequently, the above-described problems have never yet been solved.
In the prior art of Japanese Unexamined Patent Application Publication No. 2002-170330, a process is carried out for identifying whether a bit stream pertains to a PCM signal or to a DTS signal. In the specification, however, there is not any further description as for the Dolby sound. Consequently, the above-described problems have never yet been solved.